Common dispensers, such as a syringe dispenser, often include a barrel or tube for holding a material, fluid, medicine, or other medicament. The barrel or tube may have a needle or other injection member on one end and include a fitment on the other end for securing to the dispenser or dispenser body. The dispenser may include a piston within the barrel for dispensing the material out of the needle or other injection member. The piston is usually connected to a plunger rod that effects the advancement of the piston in the barrel.
Dispensers often include a mechanism to engage and disengage the plunger rod to lock or free the rod from movement. Such mechanisms in prior syringe dispensers commonly used multiple springs or multiple biasing members. Due to the stress on the multiple springs or biasing members in such systems, over time, these mechanisms may be less effective or prone to failure.